TAMPA — In her 20 years as a medical examiner, Dr. Laura Hair has seen fractures at the base of victims' skulls in only the most severe circumstances. She's found them in people who died in airplane crashes, in falls from multistory buildings, and in horrific car accidents. She's seen them in people who jumped to their death from the Sunshine Skyway Bridge.

Questioned on Friday in the murder trial of Richard McTear Jr., who is accused of throwing his ex-girlfriend's baby out the window of a moving car onto the side of an interstate, Hair said she couldn't determine exactly how the infant died. Death being an inexact science, she allowed it was possible, as the defense suggested, that the baby had been dropped onto a concrete sidewalk. But she said 3-month-old Emanuel Murray's body had suffered extreme trauma. She ruled his death a homicide.

"I have seen babies that have been hit against a wall and a dresser and everything, but I haven't seen injury that severe," said Hair, Hillsborough's deputy chief medical examiner.

Discovered by a TV news photographer who was driving to work in the early hours of May 5, 2009, Emanuel was found on the right shoulder of Interstate 275 South. He had multiple skull fractures, including at the base of his skull, where even in very young children the bone is particularly difficult to break. His brain was lacerated, Hair said, and he had an extensive hemorrhage that sent blood to the soft tissue around his eyes, turning them a bluish-purple color.

A prosecutor then asked how much force is needed to cause those injuries.

"It takes a lot," Hair replied.

She's seen such injuries in people who have fallen from three stories or more, she said, nothing less.

Emanuel's more superficial injuries included scrapes all over his body, from the top of his toes and his knees to his forehead, which was covered by a large blue bruise.

"Road rash," Hair said, the kind people get when they're ejected from a vehicle.

In all likelihood, she said, the skull fractures and skin abrasions occurred at the same time. The child probably died instantaneously, she said.

Throughout the trial, defense attorneys have argued there is no evidence that anyone, much less McTear, threw a baby onto the interstate. No one witnessed the alleged act, they said, and the medical examiner can't prove it definitively. Rather, McTear's defense has proposed that Emanuel was accidentally dropped onto the sidewalk outside of his mother's apartment as she ran out the door. They've offered no explanation for how the baby wound up face-down on I-275.

"There are two possible scenarios here," said Assistant Public Defender Theda James. "Road rash is just one possible scenario."

"Yes," Hair said, but, "I'm not sure what another cause would be."

Prosecutors said they plan to introduce DNA evidence early next week, showing that blood splotches found on the shorts McTear was wearing at his arrest are a match to Emanuel. They have also found Emanuel's blood on the center console of a car McTear, 26, is suspected of using. The car, a 1997 Chevy Malibu, belongs to his cousin Michelle Higgins, who was forced to testify on Friday over her objections.

Higgins said that in May 2009, McTear was living with her, along with several other relatives. That month, the keys to her car went missing.